Ventilator tangential blade fans have been in use since at least the 1920's and are designed to move large quantities of air efficiently. Most fan blades are shrouded in a housing and are designed to operate at a fixed speed. Typically, these fans operate with a low static pressure. Air enters axially through an inlet and is turned approximately 90.degree. to enter the minimum flow area between the blades. The air is then turned again by contact with the blades, which are also at an angle with respect to the path of air flow. Finally, air is turned as it is exhausted from the fan in a generally radial direction.
While fans of this type are classified by some as centrifugal compressors, there is a marked difference between ventilating fan pressure ratios, which do not generally exceed 1.015, and centrifugal compressors which operate at pressure ratios as high as 3.0. Conventional designs of prior art ventilator fans have, for the most part, been made with a flat plate to which is added a riveted hub. An inlet face is also provided, with blades extending between the flat plate and hub and the inlet face. Because of the large variety of bore sizes in the industry, it may be necessary to stock over 1,000 wheels.
With conventional ventilator fan designs, efficiency has not been uniformly achieved. Oftentimes large energy losses are experienced simply because the fan is not properly balanced on the motor. When conventional designs are assembled, with large riveted hubs and individually welded blades, a great deal of time is expended by skilled workers in balancing the fan by a trial and error method. More importantly, at the present time there is no really effective way to evaluate the many variables of design once the air flow, power and inlet pressure requirements are set for new or existing designs.
In designing a new fan system or fitting a fan device into an existing ventilation system, the first step is to identify the parameters of the system. It has been found that the criteria which determine the system are the flow rate, horsepower, speed and pressure drop. From this set of criteria certain variables exist which must be selected or determined to create a fan useful with those criteria. For example, the given criteria for a particular system may be met by a fan with nine blades or ten, or twelve blades. Similarly, a fan that is of an axial length of six inches and a different fan with an axial length of ten inches may both accomplish the goals of the system. However, the actual space available for replacement of the fan device and other factors may cause the designer to eliminate designs which are too tall or where the diameter is too large or too small. As a result, only a few selected designs will be available for practical consideration.
The prior art does not provide any method for selecting the optimum fan design for ventilation exhaust systems. Ness U.S. Pat. No. 1,637,652 discloses a fan or blower having a plurality of blades between a plate having a hub and an inlet. The blades are arcuate in cross section. This generally represents the fan design that has existed since at least the mid 1920's. Curved blades or blades with a variable pitch are shown in Valentine, U.S. Pat. No. 2,201,947. Two other turbine type blower wheels are shown in Dybvig, U.S. Pat. No. 3,179,329 and Jenson, U.S. Pat. No. 3,507,581.
The foregoing prior art patents all describe conventional fan devices which have certain limitations and draw backs such as those discussed above. Dybvig, for example, spot welds blower blades to mount them, thus making it difficult to balance the blades if long term operation and efficiency is desired. Dybvig, of course, is directing air in a conical direction and is not a true exhaust or ventilating systems. None of the known prior art actually addresses the design factors which contribute to optimization of exhaust or ventilation systems. There is no criteria set forth which allows one direct comparison of fan devices, except perhaps by trial and error. Two fan devices might both be tried in a system and energy cost, maintenance, noise, or other measurable factors may or may not show which system is more effective, depending in part on the weight given each factor. There is no way to determine in advance whether either design will be effective, nor can the two designs be compared without experimentation.
Accordingly, it is an object of this invention to provide an optimized manufacturing process for producing useful and reliable fans devices.
Another object of the present invention is to provide a fan device which is balanced both radially and axially, and which has increased concentricity and reproducability.
Yet another object of the present invention is to provide a fan device which is most efficient for a given flow rate, power requirement, air speed and air pressure drop.
Other objects will appear hereinafter.